4.13 Incomplete Objects

When ( or [ is typed to begin entering a complex number or
vector, respectively, the effect is to push an incomplete complex
number or vector onto the stack. The , key adds the value(s) at
the top of the stack onto the current incomplete object. The )
and ] keys “close” the incomplete object after adding any values
on the top of the stack in front of the incomplete object.

If several values lie on the stack in front of the incomplete object,
all are collected and appended to the object. Thus the , key
is redundant: [ 2 <RET> 3 <RET> 2 * 9 ]. Some people
prefer the equivalent <SPC> key to <RET>.

As a special case, typing , immediately after (, [, or
, adds a zero or duplicates the preceding value in the list being
formed. Typing <DEL> during incomplete entry removes the last item
from the list.

Incomplete entry is also used to enter intervals. For example,
[ 2 .. 4 ) enters a semi-open interval. Note that when you type
the first period, it will be interpreted as a decimal point, but when
you type a second period immediately afterward, it is re-interpreted as
part of the interval symbol. Typing .. corresponds to executing
the calc-dots command.

If you find incomplete entry distracting, you may wish to enter vectors
and complex numbers as algebraic formulas by pressing the apostrophe key.